Two-way communication system



Jan. 2, 1951 L. PRAHM 2,536,820

TWO-WAY COMMUNICATION SYSTEM Filed Sept. 17, 1948 AMPLIFIER STA 5 SUB- . STATION STA 6 SUB- STATION STA7 v 71f STATION STA4 STATION 4 INVENTOR. LOUIS PRAHM AGENT Patented Jan. 2, 1951 UNITED STATES PATENT OFFICE k, 2,536,820 'TWG- WA'Y t?GMMUNICA'IIION SYSTEM JIlouis :Pra-hm, New York, N. Y. Application September 17, 1948, Serial No. 49,749

4 Glaims.

The present invention relates to two-way communication-systems or the type referred to' in my co-pending application Ser. No. 37,789, filed July 9.1948. In that application '1 have disclosed a system wherein a plurality o'f'sta tions may selectively cornmurncate with one another, each station being equipped with a three-positionkey and with means such as a dial for automatically selecting a desired station. The three-position key has one passive position and two active positions including one .for receiving a message from a called station and another for directing a message tosuch station. I By means of this ke the calling party retains full control of the connec tion, whereas the called party need not go near the responding apparatus in order to participate in the conversation.

The general object of the present invention is to provide a simplified system of the above character, adapted particularly for installations having a small number of stations, which enables a caller at one station to communicate with a desired other station without the intermediary of an exchange, for example by actuating a push button assigned to the desired station;

Another object of the present invention is to provide a system of the oharacter'described having one or more main stations and a number of substations, each main station being adapted to call any other main station or substation while each substation is capable of responding to calls from a main station only.

The above and other objects of the invention will become apparent from the following description of a preferred embodiment, reference'being had to the accompanying drawing the sole figure of which represents a system having two main stations and five substations.

The main'stations are indicated at STA'I and STA2; the substations are indicated at STA3 through STA'I.

As in the system disclosed in my above-identified application, there is providedin the present system an amplifier 20 common to all the stations of the system, this amplifier being provided with an input circuit shown as a transformer '2! and an output circuit shown as a transformer 22. The primary of input transformer 21 and the secondary of output transformer 22 each have one terminal grounded at conductor 23. Conductor 23 is connected to a wire I3 of a multiple comprising wires Ithrough I4.

A relay 24 is adapted, when energized, to connect to the amplifier 20 its power supply, shown here as a battery 25. relatively low voltage, is connected with its positive pole to groundat conductor 23 and with-its negative pole to a conductor 21 connected, in turn, to wire 9 of the multiple. Asecond relay 2-8 is connected between wires23 and I2 and is shunted by a resistor 29, designed to act as a spark quenching means. The circuit for relay is completed by a conductor 30 connected to wire I4.

A second battery 26, of a The fourteen wires 'IIII through -I I4 leading to tation STA'I are connected, respectively, to wires I through I4of the multiple; a similar set of wires, 'Z'Eil through 21 4, connect station STAZ to the multiple. Substation 'S'IA3 is connected to wires 8, H and I3, as are the other substations STA I through STA'I, as well as to wire 3; these connections lead over wires 393, 3-98, 31 I and 3'43. Station STA I is equipped with lead-in wires M8, "ti I, 4 I 3 and 4M, the latter leading to wire '4. In'analogous manner, wires 505, 568, 5H and his are provided for station STAB, wires 6% 663, 5H and tilt for station STAG and wires TEI'I, I08, I II and H3 for station 'STA 'I. 1

Each station is equipped with a call relay designated I3] at station STA], 23I at station 'STAZ and 33I at station S'IAt. Each station has also a transducer I32, 232, 332 serving both as a loudspeaker and as a microphone. An indicator lamp I33, 233, 333 is connected in series with the respective call relay.

Each main station (STAL-S'IA2) is also provided with a control key ltd, 2135 having four contact'springs I35, its, I37, I38 and 235, 236, 232 and 238. This key has three positions, the

' first or unoper-ated position being shown at station STAI and the two operated positions at STAZ in full and dot-dash lines, respectively. Key I35, 234 is also provided with an insulated stud I39, 239 which in the third position of the ke opens a contact I40, 2%, respectively; this contact remains closed in the first two positions of the key.

A station may also be provided with a cut-out switch such as shown at II for station STAI, serving to prevent a caller (e. g. at STAZ) from listening in on a conversation going on at the location of station STAI or from transmitting a message to that station when the subscriber there desires not to be disturbed. A busy lamp I42, 242 is inserted in conductor I It, 2 I4, respectively, and is effectively in series with relay 2d as will subsequently appear.

Each main station is further provided with a set of push-buttons (six in the present case) shown at 102a through III'Ga (STAI) and Mia, 203a through 205a STAZ), designed to connect wire I63, 258; respectivelyto corresponding wires I02 through Hi5 and 20!, 203 through 266.

It will be understood that additional signaling means, for example a buzzer, may be connected in series or in parallel with the signal lamp I33 etc. in order to attract the attention of a party at a called station.

The operation of this system is as follows:

Call between two main stations.-Let us assume that a caller at station STAE desires to tall; to a party at station SIA'I. He depresses key 234 into the second (horizontal) position shown in full lines. Springs 235, 236, 23?, 1238 make their front contacts but contact 2 58 remains closed. Relay 26 energizes: Battery 28, wires 2?, 31, 23% spring 236 and front contact thereof, lamp 242, wires 2M, I l, 30-, relay 2d, ground. Relay as operates and connects power to the amplifier 20. At the same time the busy lamp in station STAI lights up in parallel with lamp 242: Wires I4 and H4, lamp I42, wires I09, 8 and 268. Re lay 28 operates: Battery 26, wires 21, 9, 269, spring 23'! and front contact thereof, closed contact 2%, wires 2 I2 and I2, relay 28 to ground.

The caller depresses momentarily his button 20m, assigned to the desired station STAI. At

the called station relay i3| energizes and lamp I33 lights: Battery 26, wires 27, 9, 269, spring 236 and front contact thereof, wire 268, button 2IlIa, wires 2!, I, IOI, relay I3I, lamp 133, Wires H3, I3, 23 to ground. Relay l3I operates and locks over its right-hand armature and front contact, wires H38 and 3 to wire 268, independently of push button 26I a which may now be released.

If switch MI is open at station STAl, nothing further will happen except that the party thereat is apprised of the fact that a caller is attempting to establish a connection; as soon as this switch is closed, a circuit is established to connect transducer I 32 across the primary of input transformer 2!: grounded primary terminal, wires 23, I3, H3, front contact and left-hand armature of relay I3 I, switch i i I, back contact and spring I 35 of key I34, transducer I32, spring H33 and back contact of key 34, wires HI and l I, upper armature and front contact of relay 28, ungrounded primary terminal. An oral response by the called party will now be heard by the caller at station STA2 where the transducer 232 is connected across the secondary of output transformer 22: Grounded secondary terminal, wires 23, I3, 2J3, front contact and spring 235 of key 234, transducer 232, spring 238 and front contact of key 234, wires 2i 3 and I8, lower armature and front contact of relay 28, ungrounded secondary terminal.

When the caller desires to transmit a message to the called station, he depresses key 234 into its third position, thereby opening contact 243. Relay 23 releases and reverses the connections to the amplifier, so that the primary of transformer 2I is now connected across the transducer 232 while the secondary of transformer 22 is connected across transducer I32. By manipulating his key 234 between the two positions indicated, the caller will be able selectively to transmit and receive messages to and from the called station STAi.

When the conversation has ended the caller releases key 234 which rises to its normal or inactive position; all relays release, and the circuits return to normal.

Call to substation.-Let us assume that the caller desires to converse with a party at station STA3. After the key 234 has been brought into horizontal position, leading to the energization of relays 24 and 28 as previously described, the caller depresses push button 263a which is the one assigned to substation STA3. Relay 33I energizes in series with lamp 333: Battery 25, wires 27, 9, 209, spring 236 and front contact thereof, wire 268, button 263a, wires 233, 3, 383, relay 33I, lamp 333, wires 3I3, I3, 23 to ground. Relay 33I attracts its armatures and connects transducer 332 across the primary of input transformer 2I Grounded primary terminal, wires 23, I3, 3I3,

front contact and lower armature of relay 33E, transducer 332, wires 3 and II, upper armature and front contact of relay 28, ungrounded primary terminal. When the key 234 is fully depressed, relay 28 will again reverse the connections and connect transducer 332 across the secondary of output transformer 22.

In completely analogous manner, actuation of any other button on station STA2 will connect that station with a selected one of substations STA4 through STA! and similar connections may be established from station STAI. It will be understood that the number of main and substations may be difierent from that shown in the drawing, although, for practical considerations, I prefer to limit a system according to the invention to a maximum of eight stations. The connections necessary between the multiple and each main station (wires I0! through I I4, for example) may then be efiected by means of two multicore cables, whereas in the case of each substation a single such cable will sufiice.

Although the invention has been described with reference to a single, preferred embodiment, it is to be understood that the same is susceptible to numerous adaptations and modifications without departing from its spirit and scope as defined in the objects and in the appended claims.

I claim:

1. In a communication system comprising a number of stations including a plurality of control stations each adapted to'call any other of said stations, in combination, an amplifier common to all of said stations, said amplifier having an input and an output circuit, a first and a second communication channel common to all of said stations, and call control means at each of said control stations comprising a key having a normal position and two ofi-normal positions including a listening and a talking position, first contact means closed in the off-normal positions of said key for connecting the respective control station to said first channel, second contact means closed in the normal position of said key for selectively connecting said respective control station to said second channel, selector means for connecting any one of the remaining stations to said first channel, and switch-over means controlled by said key for connecting said input and output circuits to said first and second channels, respectively, in one of said oiT-normal positions and to said second and first channels, respectively, in the other of said off-normal positions.

2. The combination according to claim 1 wherein said switch-over means comprises a relay common to all of said control stations, said relay having a plurality of energizing circuits each adapted to be closed by a respective one of said keys.

3. The combination according to claim 2 wherein said energizing circuits are closed in the listening positions of the respective keys.

4. The combination according to claim 1 wherein at least one of said control stations is provided with circuit breaker means operable at the will of a party thereat for disconnecting said control station from said second channel.

LOUIS PRAHM.

' REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,162,369 Campbell June 13, 1939 2,249,456 Campbell July 15, 1941 2,269,144 Campbell Jan. 6, 1942 2,317,358 Campbell Apr. 27, 1943 2,339,678 Campbell Jan. 18, 1944 2,347,079 Campbell Apr. 8, 1944 

